Moved renderer RAII helpers to their own file and added ones for clip rect and viewport

Do note that setting an empty rect in render_raii_rect_setter_base is not the same as passing nullptr.
If an empty rect is passed to SDL_RenderGetClipRect, for example, you can end up with nothing drawing
since everything is being clipped.

projectfiles/CodeBlocks/wesnoth.cbp

@@ -1009,6 +1009,7 @@
 		<Unit filename="../../src/sdl/point.cpp" />
 		<Unit filename="../../src/sdl/point.hpp" />
 		<Unit filename="../../src/sdl/rect.cpp" />
+		<Unit filename="../../src/sdl/render_utils.hpp" />
 		<Unit filename="../../src/sdl/surface.cpp" />
 		<Unit filename="../../src/sdl/surface.hpp" />
 		<Unit filename="../../src/sdl/texture.cpp" />

src/gui/core/canvas.cpp

@@ -31,6 +31,7 @@
 #include "gui/core/log.hpp"
 #include "gui/widgets/helper.hpp"
 #include "sdl/rect.hpp"
+#include "sdl/render_utils.hpp"
 #include "video.hpp"
 #include "wml_exception.hpp"
 

src/sdl/render_utils.hpp

@@ -0,0 +1,108 @@
+/*
+   Copyright (C) 2017 the Battle for Wesnoth Project http://www.wesnoth.org/
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY.
+
+   See the COPYING file for more details.
+*/
+
+#pragma once
+
+#include "sdl/rect.hpp"
+#include "sdl/texture.hpp"
+#include "video.hpp"
+
+#include <SDL_rect.h>
+#include <SDL_render.h>
+
+#include <cassert>
+
+/**
+ * Sets the renderer output target to the specified texture.
+ * @todo: add support for restoring last target.
+ */
+class render_target_setter
+{
+public:
+	explicit render_target_setter(texture& t)
+		: renderer_(CVideo::get_singleton().get_renderer())
+	{
+		if(renderer_) {
+			// Validate we can render to this texture.
+			assert(t.get_info().access == SDL_TEXTUREACCESS_TARGET);
+
+			SDL_SetRenderTarget(renderer_, t);
+		}
+	}
+
+	~render_target_setter()
+	{
+		if(renderer_) {
+			SDL_SetRenderTarget(renderer_, nullptr);
+		}
+	}
+
+private:
+	SDL_Renderer* renderer_;
+};
+
+using sdl_rect_getter = void (*)(SDL_Renderer*, SDL_Rect*);
+using sdl_rect_setter = int (*)(SDL_Renderer*, const SDL_Rect*);
+
+/**
+ * Base class for renderer RAII helpers that operate on SDL_Rects.
+ *
+ * @tparam G             Getter function. Will fetch the current applicable rect.
+ *                       That will be restored as the applicable state once this object is destroyed.
+ * @tparam S             Setter function.
+ */
+template<sdl_rect_getter G, sdl_rect_setter S>
+class render_raii_rect_setter_base
+{
+public:
+	explicit render_raii_rect_setter_base(SDL_Rect* rect)
+		: operate_(rect != nullptr)
+		, last_rect_()
+		, renderer_(CVideo::get_singleton().get_renderer())
+	{
+		if(renderer_ && operate_) {
+			(*G)(renderer_, &last_rect_);
+			(*S)(renderer_, rect);
+		}
+	}
+
+	~render_raii_rect_setter_base()
+	{
+		if(renderer_ && operate_) {
+			if(last_rect_ != sdl::empty_rect) {
+				(*S)(renderer_, &last_rect_);
+			} else {
+				(*S)(renderer_, nullptr);
+			}
+		}
+	}
+
+private:
+	const bool operate_;
+	SDL_Rect last_rect_;
+	SDL_Renderer* renderer_;
+};
+
+/**
+ * Sets the renderer clip rect.
+ */
+using render_clip_rect_setter = render_raii_rect_setter_base<
+	&SDL_RenderGetClipRect,
+	&SDL_RenderSetClipRect>;
+
+/**
+ * Sets the renderer viewport rect.
+ */
+using render_viewport_setter = render_raii_rect_setter_base<
+	&SDL_RenderGetViewport,
+	&SDL_RenderSetViewport>;

src/sdl/texture.cpp

@@ -17,9 +17,6 @@
 #include "sdl/surface.hpp"
 #include "video.hpp"
 
-#include <cassert>
-#include <iostream>
-
 static lg::log_domain log_sdl("SDL");
 #define ERR_SDL LOG_STREAM(err, log_sdl)
 
@@ -112,21 +109,3 @@ texture::info::info(const texture& t)
 {
 	SDL_QueryTexture(t, &format, &access, &w, &h);
 }
-
-render_target_setter::render_target_setter(texture& t)
-	: renderer_(CVideo::get_singleton().get_renderer())
-{
-	if(renderer_) {
-		// Validate we can render to this texture.
-		assert(t.get_info().access == SDL_TEXTUREACCESS_TARGET);
-
-		SDL_SetRenderTarget(renderer_, t);
-	}
-}
-
-render_target_setter::~render_target_setter()
-{
-	if(renderer_) {
-		SDL_SetRenderTarget(renderer_, nullptr);
-	}
-}

src/sdl/texture.hpp

@@ -80,17 +80,3 @@ private:
 
 	SDL_Texture* texture_;
 };
-
-/**
- * Small RAII helper class to temporarily set the renderer target to a texture.
- */
-class render_target_setter
-{
-public:
-	explicit render_target_setter(texture& t);
-
-	~render_target_setter();
-
-private:
-	SDL_Renderer* renderer_;
-};